Fine needle aspiration cytology of a primary malignant peripheral nerve sheath tumor arising in the parotid gland: a case report.

Background: Malignant peripheral nerve sheath tumor (MPNST) is an uncommon mesenchymal neoplasm showing nerve sheath differentiation, usually arising in large nerves of the trunk and extremities. Primary location in the parotid gland is rare. We describe fine needle aspiration (FNA) findings in a case of MPNST in the parotid gland. Differential diagnostic problems encountered in interpretation are discussed.

Case: A 39-year-old man underwent FNA of a well-circumscribed, painless, mobile mass of the parotid gland. Smears were cellular, with clusters of tightly packed spindle or oval cells arranged in a storiform or whorled pattern, showing clearly malignant features. Elongated nuclei with tapered ends and many angulated nuclei were encountered. The background contained abundant necrotic material with dispersed malignant nuclei. Neoplastic cells were positive for vimentin and weakly positive for S-100 and negative for cytokeratins 8 and 18 and HMB-45. Cytologic diagnosis was positive for malignant cells consistent with a spindle cell sarcoma, with morphologic features compatible to neural differentiation, confirmed by histologic examination.

Conclusion: This case illustrates that attention to moiphologic criteria suggestive of nerve sheath phenotype supported by immunocytochemical data is extremely helpful and reliable in the diagnostic approach to MPNSTs, even in rare locations.